The hypothesis that CSF secretion by the choroid plexus may be significantly reduced or absent in kaolin-induced hydrocephalic cats will be examined. In these experiments, the volume flow of fluid into the cerebral ventricles will be measured by lateral ventricle-to-lateral ventricle perfusion, the osmolality of serum is reduced, the volume flow fluid into the ventricles should be relatively less and be a constant amount when compared to normal animals with a functioning choroid plexus. CSF formation on the hydrocephalic cat will also be measured both with and without the use of acetazolamide, a drug known to inhibit CSF secretion by the choroid plexua. In all experimentally obstructed hydrocephalic cats, communication between the ventricular system and the subarachnoid space is re-established by the dilated spinal cord central canal. Therefore, in both acute and chronic hydrocephalus, a laminectomy and splitting of the dura will be carried out at various levels of the cord to determine whether the central canal can dilate to the same degree as do the cerebral ventricles when the calvarium is removed.